RRS should have a look at the Milich grip and learn how to make the metal possible to hold without slipping. I had to attache some anti slip tape on the grip handle and now it works as expected (which means very very well and the grip won't come off the camera).

Curious about where you placed the tape... On the "inside" of the grip where your fingertips rest, or on the "front face" rounded part of the grip. I'm happy with the feel of mine, but like to see ideas from others for improvement. Photo?